Figure 11: The pathophysiological classification of congenital gastric outlet obstruction due to pyloric atresia or gastric web5. 1 = antral gap atresia, 2 = pyloric gap atresia, (type 1), 3 = pyloric gap atresia, (type 2), 4 = pyloric septum (solid atresia), 5 = pyloric gap atresia (type 3), 6 = pyloric membrane (type 1), 7 = pyloric membrane (type 2), 8 = antral membrane (web), 9 = antral membrane (wind sock).
The etiology of pyloric atresia is unknown. According to Tandler12 this anomaly is the consequence of a failure of the tube to canalize during development. Lowe and Bernard13,instead, advance a mechanical cause or vascular injury. While there is no experimental evidence in support of these two theories, both are thought to explain this intestinal anomaly. In the forms associated with epidermolysis bullosa, Weber11 holds that the lesion results from an intrauterine mucosal injury within junctional epidermolysis bullosa, with subsequent peptic digestion and an inflammatory scarring reaction; however, hystological examination of the pylorus carried out in one case at the 18th week of gestation did not evidence an inflammatory reaction.
The fetal esophagus is usually situated between C11 and T9, but it escapes ultrasound imaging because it is closed during the non- functioning period, while it is dilated during swallowing. A prenatal diagnosis of congenital gastric outlet obstruction may be suspected in cases with gastric distension and polyhydramnios (61%), or in couples with risk of epidermolysis bullosa or familial occurrence of pyloric atresia. However, specific ultrasound pictures have not yet been described.
On the basis of our observations, we believe that the ultrasound markers of this anomaly could be gastric distension and esophageal hypercontractility, which is seen with real-time scans. A longitudinal scan of the chest and abdomen (fig. 2,3,6,7) shows the markedly distended stomach and the presence of a tubular, smooth-walled, anechogenic, contractile formation. This tube originates in front of the spine to reach the upper third of the trunk, crosses the chest behind the heart and terminates in the stomach. This tubular structure is the esophagus dilated by amniotic fluid, and on real-time scan it shows an irregular peristaltic activity that corresponds to the mechanism of fetal suction and swallowing. As the swallowing and suction mechanisms are not altered, the fetus continues to swallow the amniotic fluid, which is then regurgitated due to the pyloric obstruction, thus creating an important gastroesophageal reflux. A transverse scan of the chest, with a subcostal "four chamberâ€ view (fig. 8,9), further confirms the diagnosis because the esophagus is seen as an anechogenic, round, peristaltic mass situated between the descending aorta and the superior wall of the left atrium.
The differential diagnosis with other upper gastrointestinal tract anomalies is based on the presence of polyhydramnios (61%), a dilated stomach and esophagus, and peristaltic esophageal waves on real-time. In esophageal atresia with or without fistula, there is no or very little fluid in the upper gastrointestinal tract. In this case, real-time ultrasonography visualizes the esophagus proximal to the site of atresia, which alternates between filling and emptying14. Esophageal atresia may also be accompanied by other malformations of the gastrointestinal tract, as well as by malformations of the heart, vertebrae, limbs and kidneys (VATER syndrome)15. Thus, the identification of any one of these abnormalities facilitates the differential diagnosis. While the classic "double bubbleâ€ is seen in the case of duodenal atresia, the findings may become less clear when esophageal atresia without fistula (4%) is present. In this case, the classic "double bubbleâ€ sign is not present.
The prognosis depends on the gestational age and birth weight, as well as the presence or absence of associated congenital anomalies or epidermolysis bullosa. In cases without other malformations, the prognosis is usually good. Only a few reports describe rupture of the stomach17 and aspiration pneumonia as the result of a delay in the diagnosis. Prematurity and low birth weight with respiratory complications (hyaline membrane disease) are thought to be related to polyhydramnios, causing preterm labor. The prognosis is unfavorable when both pyloric atresia and epidermolysis bullosa are present. The prenatal diagnosis of isolated pyloric atresia should greatly improve the prognosis, compared to cases diagnosed after birth.
Familial occurrence has been reported, and an autosomal recessive transmission has been advanced9-10.
Since prenatal diagnosis of pyloric atresia has not been previously reported and considering our two cases, we believe that obstetrical management should not change. Polyhydramnios may contribute to the onset of premature labor; tocolytic agents are indicated in these patients and amniotic fluid drainage may also be considered. The antenatal administration of steroids in cases of lung immaturity is indicated. Genetic counseling must be offered to couples with pyloric atresia-epidermolysis bullosa syndrome, since the risk of an affected child is 25%.
Epidermolysis bullosa can be diagnosed prenatally at the 18th week of pregnancy with a skin biopsy performed via fetoscopy. Given the high neonatal mortality rate of this syndrome, couples should be given the option to terminate the pregnancy in due time. Delivery in a specialized center is recommended, as these infants will require immediate surgical care.
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